1. Field of the Invention
This invention relates to a golf ball.
2. Description of the Related Art
Conventionally in a golf ball, plural kinds of dimples have been disposed on a spherical face in various design patterns for improving the flying ability of the golf ball. Furthermore, a great circle zone not crossing the dimples, namely, a seam line is on a position of the spherical face corresponding to a parting line of a metal mold for production of the golf ball.
The existence of the seam line, however, is a cause of aerodynamic asymmetry of the golf ball. That is to say, it is known that relatively great differences are generated in flying distance and flight time when the rotating direction (flying direction) of the ball corresponds to the seam line and when the rotating direction of the ball corresponds to a circumferential direction at right angles with the seam line. Therefore, it has been the aerodynamic symmetry of the golf ball by forming many great circle zones not crossing the dimples similar to the seam line on the spherical face, for example, a golf ball of geometrical high uniformity, in which a spherical face is divided with polyhedrons or quasi-polyhedrons, and dimples are disposed line-symmetrically in spherical polygons (Japanese Patent Provisional Publication No. 8-10355).
In a golf ball having many great circle zones on a spherical face, however, there is a defect in that flying distance decreases due to remarkable reduction of dimple effect because of the high probability of correspondence of a rotating direction of the golf ball and a direction of the great circle zone (not having dimples). Furthermore, there is another problem in that the degree of freedom of design is very low because there are a limited number of patterns which can divide the sphere with polyhedrons or quasi-polyhedrons, and the dimple disposition is line-symmetric in the spherical polygons. Therefore, the dimple disposition still needs to be improved.